In semiconductor wafer processing, it is often required to process and/or test a wafer over temperature. Temperature-controlled wafer chucks have been developed to support a wafer and cycle the wafer over temperature during testing and/or processing. In a typical temperature-controlled wafer chuck, a temperature control module such as a heater and heat sink assembly is provided as a layer in the chuck. A top surface on which the wafer is mounted is provided at the top of the heater and heat sink assembly, and a base by which the chuck is mounted to the host apparatus, e.g., wafer prober, is provided beneath the heater and heat sink assembly. In some heater/heat sink assemblies, thermoelectric modules, also known as Peltier devices, are used to provide the temperature control. Peltier devices are small solid-state devices that function as heat pumps. The typical device is a sandwich formed by two ceramic plates with an array of small bismuth telluride (Bi2Te3) cubes in between. When a DC current is applied, heat is moved from one side of the device to the other, where it is removed with a heat sink. The cold side of the device is commonly used to cool a wafer. If the current is reversed, the device can be used as a heater by moving heat in the opposite direction.
One drawback to Peltier devices is that they are subject to mechanical stresses. These stresses can come from different sources. In one case, mechanical stresses induced by expansion and contraction of chuck layers over temperature can cause the devices to become unreliable and eventually fail. This is particularly true in wafer chucks where the Peltier devices are rigidly attached to one or both of the upper and lower layers of the heater/heat sink assembly. As the assembly expands and contracts, the Peltier devices fail due to the mechanical stresses induced by thermal effects.
In another case, the mechanical stress induced by differential expansion of the ceramic top and bottom layers of the device itself can cause the devices to become unreliable and fail. This is particularly true if the Peltier modules are large in size. The larger devices create increased differential expansion and therefore develop more mechanical stress.